Bring a large pot of generously salted water to a rolling boil. Add rigatoni and cook until 1 minute shy of al dente (about 10 to 11 minutes). Before draining, dip a measuring cup in to reserve 1/2 cup of hot, starchy pasta water, then drain the pasta.

While the pasta boils, heat 2 tablespoons olive oil in a wide 12-inch deep skillet over medium heat. Add the fresh sage leaves in a single layer and sizzle for 45 to 60 seconds until fragrant and crisp (do not let them brown too deeply). Transfer crispy sage leaves with a fork to a paper towel-lined plate, leaving the aromatic sage-infused oil in the pan.

Add the remaining 1 tablespoon olive oil and minced garlic (plus red pepper flakes if using) to the skillet. Sauté over gentle medium-low heat for 60 seconds until fragrant without burning.

Whisk in the pure pumpkin purée and vegetable broth until completely smooth. Stir in the heavy cream, freshly grated nutmeg, sea salt, and black pepper. Bring to a gentle simmer for 3 to 4 minutes until the sauce thickens into a glossy, velvety orange cream.

Tumble the hot drained rigatoni into the simmering pumpkin sauce. Add the freshly grated parmesan cheese and splash in 1/4 cup of the reserved hot starchy pasta water.

Toss vigorously with a wooden spoon over low heat for 1 to 2 minutes until the cheese melts and the sauce clings tightly to every ridge of the rigatoni. (Add a splash more pasta water if you prefer a silkier texture). Plate into warm pasta bowls, top with the crispy fried sage leaves and extra shaved parmesan, and serve immediately!